1. Field of the Invention
The present invention relates to an endoscope shape analysis apparatus, and particularly to an endoscope shape analysis apparatus having a coordinates obtaining portion for detecting coordinate values in a plurality of places.
2. Description of the Related Art
An endoscope is adapted to externally insert an elongated insertion portion having flexibility into a test portion, which is a lumen in a body cavity, to observe the test portion and perform necessary treatment. But, the lumen in the body cavity is bent as observed in a large intestine and a small intestine, and an operator can not easily see to what position the inserted insertion portion is inserted, or in what shape the inserted insertion portion is. Therefore, conventionally, a test body portion into which the insertion portion is inserted is externally irradiated with X-rays to detect an insertion state, such as a position and shape of insertion of the insertion portion into a lumen. But, the X-rays are not harmless to a human body. Besides, an irradiation place is limited, and therefore, the X-rays are not always preferred as a method for detecting the insertion state of the insertion portion.
Accordingly, an apparatus and method for detecting an insertion state of an endoscope or a catheter are proposed in which by disposing a plurality of magnetic field generating devices in an insertion portion and using a magnetic field sensing portion outside a body cavity, without having a physiological adverse effect on a human body, a state of insertion of the insertion portion into a lumen in the body cavity can be detected. Further, when the insertion portion is inserted into a large intestine and the like, the insertion portion may form a spiral loop in a free portion where the intestine is not fixed to an abdominal cavity and the like. Insertion operation in such a state in which the insertion portion forms a loop, that is, a state in which the intestine is deformed in a loop shape, causes pain to a patient. Therefore, Japanese Patent Application Laid-Open Publication No. 2000-175861 discloses an endoscope shape detection apparatus that can recognize occurrence of a loop of an insertion portion during insertion and generate a warning to an operator.
Also, Japanese Patent Application Laid-Open Publication No. 2003-245242 discloses a method in which since a number of magnetic field generating devices disposed in an insertion portion to measure a shape of the insertion portion is limited, a position of the insertion portion between magnetic field generating devices is made up for by an interpolation process.
The endoscope shape detection apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 2000-175861 detects a shape of an insertion portion by a combination of a plurality of magnetic field generating devices disposed in the insertion portion, and a magnetic field sensing portion outside a body cavity.
As shown in FIG. 1A, the endoscope shape detection apparatus can obtain three-dimensional coordinates of, for example, eight magnetic field generating devices C1 to C8, by a combination of the plurality of magnetic field generating devices disposed in the insertion portion, and a magnetic field sensing portion outside a body cavity. The endoscope shape detection apparatus can sense a shape of the insertion portion by interpolating for coordinate points, as shown in FIG. 1B.
Position information of a winding direction of the loop is very important for an operator because a rotation direction of the insertion portion operated by the operator to eliminate the loop is different depending on the way in which the loop is wound, as shown in FIG. 2.
FIG. 2A shows a loop in which a distal end portion 20a side of the insertion portion 20 is closer to the operator than a proximal end portion 20b side. To eliminate the loop shown in FIG. 2A, the operator needs to rotate the proximal end portion 20b side of the insertion portion clockwise. On the other hand, in a loop shown in FIG. 2B, the distal end portion 20a side of the insertion portion 20 is on a further side from the operator than the proximal end portion 20b side. To eliminate the loop shown in FIG. 2B, the operator needs to rotate the proximal end portion 20b side of the insertion portion counterclockwise.
A position display error phenomenon in which a way in which a loop of an insertion portion is wound is erroneously reversely displayed is called “slipping through” because, for example, a change from a state in which the insertion portion on a distal end side is at a position closer to an operator than the insertion portion on a proximal end side (FIG. 2A) to a state in which the insertion portion on the distal end side is at a position farther from to the operator than the insertion portion on the proximal end side (FIG. 2B) is seen as if the insertion portion on the distal end side slips through the insertion portion on the proximal end side.
Further, even if a shape display of the insertion portion 20 is correctly displayed without an error, as shown in FIG. 2C, distinction as to which of the insertion portion on the distal end portion 20a side and the insertion portion on the proximal end portion 20b side is at a position closer to the operator may be difficult in an intersection portion of the loop. The discrimination difficulty phenomenon in the intersection portion of the loop is a phenomenon caused by a three-dimensional endoscope shape being displayed on a two-dimensional display screen.